Can I force Exim to relay mails with unknown recipient to another host?
I want to stage the Exim to Exchange migration in a way that would allow me to move individual accounts between servers and keeping all accounts functional.
My idea is to:
- configure Exchange to act as Internal Relay, ie. to relay unrecognized recipients to Exim,
- perform an analogous configuration on Exim and enforce any form of loop protection at either end (for messages that are unknown on both servers),
- keep Exim as MX records target until the end of staging,
- gradually create new accounts on Exchange and disable them on Exim at the same time
I'd also welcome any criticism if the idea sounds crappy for any reason.